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Re: [ccp4bb]: Cys modification

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To add to the discussion about the modified Cys:

I once collected  1.15 A data (lambda 0.9475) and found residual
density close to two of the four Cys in my protein. 
Both peaks peaks also showed up in anomalous difference maps and 
although I first thought it was something like mercury, an elemental
analysis of the samples I had used (Scanning Electron Microscopy),
there turned out to be traces of lead (Pb) in one of my samples.
If you still have your solutions left and really want to know, you might 
try to have them checked by SEM for the most likely metals.
The resulting structure (with Cys-Pb entity) is in 1b6g.

Ivo Ridder
 | Ivo Ridder                                                      |
 |                                                                 |
 | Laboratory of Biophysical Chemistry                             |
 | Department of Chemistry                                         |
 | University of Groningen                                         |
 | Nijenborgh 4                       tel   : +31(50)3634397       |
 | 9747 AG Groningen                  fax   : +31(50)3634800       |
 | The Netherlands                    e-mail: I.Ridder@chem.rug.nl |
 | URL:http://www.xray.chem.rug.nl/~ivo/ivo.html                   |